Patent application title: MULTILAYER ASSEMBLY AND METHOD FOR PRODUCING THE SAME

Abstract:

The invention relates to a multilayer tube assembly and a method for
producing the same. In particular, the present invention relates to a
multilayer tube assembly, which may be used in sanitary and heating
installations. The multilayer tube assembly according to the present
invention comprises a seamless copper 1 tube provided on its external
surface with an oxide layer 2 having a thickness of 0.1 μm to 1 μm;
at least one intermediate 3 adhesive layer on said oxide layer 2
consisting basically of LLD-PB and containing 1 wt.-% to 2 wt.-% of an
additive metal deactivator; and at least one outer polymeric layer 4
provided on said intermediate adhesive layer 3 and consisting mainly of a
high-molecular polymeric material and 2 wt.-% to 4 wt.-% of an additive
flame retardant. The multilayer tube assembly is produced by a method
comprising the steps of: cleaning said seamless copper 1 tube with a
petroleum-based agent; oxidising the external surface of said seamless
copper tube 1 a) for multilayer tube assembly having an outer diameter
less than 32 mm, in an atmosphere of nitrogen and air at a temperature
range of 550° C. to 700° C., or b) for multilayer tube
assembly having an outer diameter larger than 32 mm, in atmospheric air
at a temperature of 150° C. to 250° C. and in a flame
station comprising multiple flame nozzles around the perimeter of said
tube; extruding said intermediate adhesive layer 3 onto said seamless
copper 1 tube at a temperature range of 200° C. to 230° C.;
and extruding said outer polymeric layer 4 onto said intermediate
adhesive layer 3 at a temperature range of 210° C. to 250°
C.

Claims:

1. A multilayer tube assembly comprising:a seamless copper tube (1)
provided on its external surface with an oxide layer (2) having a
thickness of 0.1 pm to 1 μm;at least one intermediate adhesive layer
(3) on said oxide layer (2) consisting basically of LLD-PE and containing
1 wt.-% to 2 wt.-% of an additive metal deactivator; andat least one
outer polymeric layer (4) provided on said intermediate adhesive layer
(3) and consisting mainly of a high-molecular polymeric material and 2
wt.-% to 4 wt.-% of an additive flame retardant.

2. The multilayer tube assembly according to claim 1, wherein the surface
roughness Ra of said oxide layer (2) is 200 nm to 900 nm.

3. The multilayer tube assembly according to claim 1 wherein said oxide
layer (2) is obtainable bya) oxidising a seamless copper (1) tube having
an inner diameter less than 26 mm in an atmosphere of nitrogen and air at
a temperature of 550.degree. C. to 700.degree. C., orb) oxidising a
seamless copper tube (1) having an inner diameter larger than 26 mm in
atmospheric air at a temperature of 150.degree. C. to 250.degree. C. and
in a flame station comprising multiple flame nozzles around the perimeter
of said tube.

4. The multilayer tube assembly according to claim 1, wherein said
intermediate adhesive layer (3) has a layer thickness in the range from
0.05 mm to 0.15 mm.

5. The multilayer tube assembly according to claim 1, wherein said metal
deactivator is a phenolic oxidant.

6. The multilayer tube assembly according to claim 1, wherein said flame
retardant is a triazine derivative.

7. The multilayer tube assembly according to claim 1, wherein said outer
polymeric layer (4) has a layer thickness in the range from 1.5 mm to 5.1
mm.

8. The multilayer tube assembly according to claim 1, wherein copper
oxides are added to said outer polymeric layer (4) to augment the thermal
conductivity of said outer polymeric layer (4) to at least 90 W/mK.

9. The multilayer tube assembly according to claim 1, wherein external
corrugations are formed in said outer polymeric layer (4) bya) specially
designed extrusion dies, orb) the use of embossed rolls after extrusion
has taken place.

10. A method for producing a multilayer tube assembly comprising the steps
of:cleaning said seamless copper (1) tube with an oxidising
agent;oxidising the external surface of said seamless copper tube (1) a)
having an inner diameter less than 26 mm in an atmosphere of nitrogen and
air at a temperature range of 550.degree. C. to 700.degree. C., or b)
having an inner diameter larger than 26 mm in atmospheric air at a
temperature of 150.degree. C. to 250.degree. C. and in a flame station
comprising multiple flame nozzles around the perimeter of said
tube;extruding said intermediate adhesive layer (3) onto said seamless
copper tube (1) at a temperature range of 200.degree. C. to 230.degree.
C.; andextruding said outer polymeric layer (4) onto said intermediate
adhesive layer (3) at a temperature range of 210.degree. C. to
250.degree. C.

Description:

BACKGROUND

[0001]1. Field of the Invention

[0002]The present invention relates to a multilayer tube assembly and a
method for producing the same. In particular, the present invention
relates to a multilayer tube assembly, which may be used in sanitary and
heating installations. It may additionally be used to transfer water in
cooling systems (fan-coolers and conditioners) in heating and cooling
installations, without the risk of condensation (dew point phenomena) for
highly energy-efficient cooling systems of buildings, as well as for the
transfer of gases (coolants, fuels and natural gas).

[0003]2. Related Prior Art

[0004]Tubes are known to be manufactured in seamless form, entirely out of
pure copper (deoxidised with phosphorus), to be used in sanitary,
air-conditioning, heating and cooling as well as gas transfer
installations. The disadvantage of this method is as follows.

[0005]1) The heat dissipates easily to the environment, as copper has a
high thermal conductivity, decreasing therefore the efficiency of central
heating systems.

[0006]2) To attain the necessary robustness for use in water supply and
heating systems, these tubes require increased mass of copper.

[0007]3) The tubes are not flexible, especially when bending is sought
without the use of tools.

[0008]4) If the tube operates in humid environment, it may be externally
attacked with the probability of tube wall perforations due to corrosion
phenomena.

[0009]5) Finally, in fan-cooling systems it is possible to have formation
of dew at the copper wall, a condition unfavourable with regard to the
endurance of the tubes (corrosion phenomenon).

[0010]Copper tubes coated with a plastic mix are widely known today to be
used for transfer of hot water in heating systems with a minimum thermal
loss to the surrounding space. These are seamless copper tubes with PVC
coating that is not adhered to the copper tube and bears grooves, in
order to allow manual processing (i.e. bending) and minimises heat loss.

[0011]The disadvantages of this method are as follows.

[0012]1) The loose interface between the two independent constituent parts
(copper and plastic) along with the air entrapped between the grooves
decrease the efficiency of under-floor heating systems.

[0013]2) The installation time is increased as the plastic coating must be
taken away in order for water-tight joints to be achieved.

[0014]3) The tubes are not flexible, especially when bending is sought
without the use of tools.

[0015]4) If the tube operates in humid environment, the grooves of the
plastic coating allow humidity to penetrate between the copper tube and
the coating and may lead to corrosion phenomena.

[0016]5) Finally, in fan-cooling systems the creation of dew on the copper
wall of the tubes is possible, an unfavourable event with regards to the
endurance of the tubes (corrosion phenomena) and to the thermal
efficiency of systems using such tubes.

[0017]Tubes are also known with a smooth plastic coating (without grooves)
whose objective is the exchange of heat between the tube and its
surroundings. The disadvantages of this method are as follows.

[0018]1) The loose interface between the two independent constituent parts
(copper and plastic), where their separating surfaces allow air to be
trapped between them decreasing the efficiency of under-floor heating
systems.

[0019]2) The installation time is increased since the plastic coating
requires to be taken away in order for water-tight joints to be achieved.

[0020]3) The tubes are not flexible, especially when bending is performed
without the use of tools.

[0021]Furthermore, tubes made of plastic and aluminium according to the
USA National Standard ASTM F 1335 are also known. They consist of
multiple plastic layers (polyethylene or other types of plastic
reinforced by multi-layer aluminium tubes). The product of this method is
inferior to the one hereby suggested with regard to the following points.

[0022]1) The dimensional tolerance range (of the diameter and the wall) is
greater, because the multiple plastic layers applied in a semi-fluid
state result in non uniform distribution of the plastic mass. On the
contrary, in the tube hereby suggested, the plastic layers are applied on
the outside of an already formed metallic tube, with stricter dimensional
tolerances, a fact that favouring uniform distribution of the plastic
semi-fluid mass.

[0023]2) Due to the aforementioned disadvantage the water tightness of the
joints of the installations is not ensured.

[0024]3) The required installation time is longer.

[0025]4) The operation of cooling, heating and hot water installations
with the system made of plastic and aluminium is less reliable and has a
shorter life span than the copper/plastic system due to the higher
coefficient of thermal expansion (fatigue and loose joints phenomena).

[0026]5) They have a reduced ability to withstand sudden pressure
increases or negative pressures of the system (water hammer or vacuum),
because the metallic part on which their stress bearing ability depends
(Aluminium) is welded, as well as because of the inferior mechanical
features of welded aluminium as compared to copper, while the metallic
part of the suggested product is homogeneous, seamless and resistant to
water hammers.

[0027]6) They exhibit lower strength to hydrostatic sustained pressure due
to their lower strength resulting from the welded metallic aluminium
tube, as opposed to the uniform metallic wall of the copper tube of the
suggested product.

[0028]7) The quality of the welded metallic tube is controlled with
difficulty as far as the resultant fusion strength is concerned, so these
tubes exhibit increased probability to develop welding failures (hidden
defects), hence decreased local strength, while the copper tube can on
the contrary be fully controlled with a highly reliable electronic system
of "eddy currents", which has excellent results in seamless tubes (100%
inspected tube).

[0029]8) Hot and cold pressure cycling leads to the delamination of the
inner plastic coating from the aluminium reinforcement (e.g. during the
supply of hot water (˜90° C.) which is caused by sudden
changes of temperature between inner and outer walls due to the limited
thermal conductivity of plastics, whereas the suggested product an the
contrary does not have an inner insulating plastic layer.

SUMMARY OF THE INVENTION

[0030]The aim of the invention is to overcome the above disadvantages of
the prior art.

[0031]It is therefore an object of the present invention to provide a
multilayer tube assembly which attains improvement in the behaviour of
both constituent parts against handling and speed of installation (e.g.
bending, connecting, adjusting), as well as takes advantage of the
combination of the optimum thermal and mechanical properties of both
materials.

[0032]Moreover, it is an object of the present invention to provide the
above-mentioned multilayer tube assembly which is resistant to high
temperatures required by closed heating systems, namely temperatures
higher than 95° C. and which withstands extreme working pressures
required by gas transfer systems of 0.01 MPa up to larger than 1 MPa.

[0033]It is a further object of the present invention to provide a method
for producing the multilayer tube assembly.

[0034]The above and other objects have been accomplished by a multilayer
tube assembly comprising: a seamless copper tube (1) provided on its
external surface with an oxide layer (2) having a thickness of 0.1 μm
to 1 μm; at least one intermediate adhesive layer (3) on said oxide
layer (2) consisting basically of LLD-PE and containing 1 wt.-% to 2
wt.-% of an additive metal deactivator; and at least one outer polymeric
layer (4) provided on said intermediate adhesive layer (3) and consisting
mainly of a high-molecular polymeric material and 2 wt.-% to 4 wt.-% of
an additive flame retardant.

[0035]Furthermore, above and other objects have been accomplished by
method for producing a multilayer tube assembly comprising the steps of:
cleaning said seamless copper tube (1) with a petroleum-based agent;
oxidising the external surface of said seamless copper (1) tube a) for
multilayer tube assembly having an outer diameter less than 32 mm, in an
atmosphere of nitrogen and air at a temperature range of 550° C.
to 700° C., or b) for multilayer tube assembly having an outer
diameter larger than 32 mm, in atmospheric air at a temperature of
150° C. to 250° C. and in a flame station comprising
multiple flame nozzles around the perimeter of said tube; extruding said
intermediate adhesive layer (3) onto said seamless copper tube (1) at a
temperature range of 200° C. to 230° C.; and extruding said
outer polymeric layer (4) onto said intermediate adhesive layer (3) at a
temperature range of 210° C. to 250° C.

[0036]In a preferred embodiment the multilayer tube assembly has the
surface roughness Ra of the oxide layer (2) is 200 nm to 900 nm.

[0037]In another preferred embodiment the oxide layer (2) is obtainable by
a) oxidising a seamless copper tube (1) in an atmosphere of nitrogen and
air at a temperature of 550° C. to 700° C. for multilayer
tube assembly having an outer diameter less than 32 mm, or b) oxidising a
seamless copper tube (1) in atmospheric air at a temperature of
150° C. to 250° C. and in a flame station comprising
multiple flame nozzles around the perimeter of said tube, for multilayer
tube assembly having an outer diameter larger than 32 mm.

[0038]It is moreover preferred that the intermediate adhesive layer (3)
has a layer thickness in the range from 0.05 mm to 0.15 mm.

[0039]According to an aspect of the present invention the metal
deactivator is a phenolic oxidant and the flame retardant is a triazine
derivative.

[0040]According to another aspect of the present invention the outer
polymeric layer has a layer thickness in the range from 1.5 mm to 5.1 mm.

[0041]In a special embodiment copper oxides are added to said outer
polymeric layer (4) to augment the thermal conductivity of said outer
polymeric layer to at least 90 W/mK.

[0042]In a further special embodiment external corrugations are formed in
said outer polymeric layer (4) by a) specially designed extrusion dies,
or b) the use of embossed rolls after extrusion has taken place.

SHORT DESCRIPTION OF THE DRAWING

[0043]FIG. 1 is a cross section showing a non-scale view of the multilayer
tube assembly according to the present invention, wherein reference
number 1 denotes the seamless copper tube, reference number 2 denotes the
oxide layer, reference number 3 denotes the intermediate adhesive layer,
and reference number 4 denotes the outer polymeric layer.

DISCLOSURE OF THE INVENTION

Production of the Seamless Copper Tube

[0044]The raw material used for the formation of the seamless copper tube
1 are solid cylinders of pure copper (billets with 99.95% Cu), which have
been deoxidised by phosphorus. The billets are pre-heated at a
temperature of approximately 900° C. to soften the copper material
in order to be pliable. The pre-heated billets are then placed in a
powerful press, where the solid billets, following a double action of the
ram, are firstly pierced and then extruded to a straight length copper
tube. The hot tube is immediately cooled down with water, to achieve room
temperature.

[0045]Subsequently, successive drawing steps of the formed copper tube
follow, through a series of dies with diameters smaller than that of the
fed copper tubes, which results in reduction of the tube diameter
following each pass. In order to thin in a controlled way at these
stages, a tool is placed inside the tube, specially shaped in a manner
that the developed frictional forces during drawing hold it steadily at a
fixed point, where the tube is funnelled through the dies.

[0046]The above mentioned processes are performed in cold state (cold
drawing) with the order as follows.

[0047]A. Manufacturing of the copper tubes for flexible pancake coils or
hard straight lengths, with dimensions of 10 mm to 26 mm in inner
diameter and 0.20 mm to 0.60 mm in wall thickness:

[0048]Straight drawing of the tubes on a drawing bench, straight drawing
in a Schumag type machine, straight drawing followed by coiling on a drum
(bull block). At this point the tube is coiled in order to attain a
circular shape (coils) for the easier transportation within the
production area and it is then transferred to a similar drawing machine
(horizontal bull block). From this point onwards, the transfer of each
coiled tube within the production plant is made in baskets. A series of
drawing passes follows, using drum type drawing machines (spinner blocks
to final dimensions of {10 mm-26 mm}×{0.20 mm-0.60} mm), where the
final dimensions of the tube to be transferred to the plastic coating
department is attained

[0049]B. Manufacturing of metal tubes for hard straight lengths with
dimensions of 26.0 mm to 97.1 mm in inner diameter and 0.50 mm to 1.50 mm
in wall thickness:

[0050]Straight drawing of tube on a drawing bench, straight drawing an a
Schumag type machine, straight drawing in drawing benches using a tapered
plug (mandrel) inside the tube, kept in fixed point in the tube
(stationary mandrel) by the means of a rod. For easier transportation
within the manufacturing site, the resulting straight lengths are cut in
smaller pieces. The final dimensions of the straight lengths, transferred
to the linear storage feeder, ahead of the plastic coating line, are {26
mm-97.1 mm}×{0.50 mm-50 mm}.

Production of the Multilayer Tube Assembly Using a Seamless Copper Tube 1
Having an Inner Diameter of 10 mm to 26 mm and a Wall Thickness of 0.20
mm to 0.60 mm

[0051]A seamless copper tube 1 (dimensions are given in Table 1) is
conveyed to an annealing furnace and heated inside the annealing furnace
in an atmosphere of nitrogen and air to a temperature of 550° C.
to 700° C. in order to oxidise the external surface. The thickness
of the oxide layer 2 is from 0.1 μm to 1.0 μm.

[0052]At this step, the seamless copper tube 1 is also internally cleaned
with blowing air therethrough. Moreover, the hardness of the seamless
copper tube is reduced.

[0053]Preferably a difference in the annealing temperature is made between
seamless copper tubes 1 produced in coils (annealing temperature
600° C. to 700° C.) and seamless copper tubes produced in
straight lengths (annealing temperature 550° C. to 650°
C.).

[0054]Subsequently the annealed seamless copper tube 1 having an oxide
layer 2 on its external surface is sufficiently cooled in ambient
atmosphere.

[0055]The seamless copper tube 1 is then passed through a first die, where
an adhesive component is extruded at an extrusion temperature of
200° C. to 230° C. through a primary extruder onto the
oxide layer 2 on the external surface of the seamless copper tube, in
order to form an intermediate adhesive layer 3 having a thickness of 0.05
mm to 0.15 mm.

[0056]No forced cooling takes place after the extrusion of the
intermediate adhesive layer 3.

[0057]The seamless copper tube 1 directly proceeds to the second die,
where a polymeric component is extruded at an extrusion temperature of
210° C. to 250° C. through a secondary extruder onto the
intermediate adhesive layer 3 formed in the above step, in order to form
an outer polymeric layer 4. The thickness of the outer polymeric layer 4
is given in Table 2.

[0058]The second die is also called the finishing extrusion die, since it
controls the final outer layer of multilayer tube assembly.

[0059]In a special embodiment, the adhesive component and the polymeric
component may be co-extruded in a single extruder die.

[0060]In another special embodiment, copper oxides may be added to the
outer polymeric layer 4 in order to augment its thermal conductivity up
to at least 90 W/mK. The copper oxides may be incorporated in a polymeric
carrier resin and may be added in the form of pellets to the polymeric
component.

[0061]In a further special embodiment, external corrugations may be formed
on the outer polymeric layer 4 of the multilayer tube assembly through a)
specially designed extrusion dies, or b) through the use of embossed
rolls after extrusion has taken place.

[0062]Subsequent to the final extrusion cooling of the multilayer tube
assembly takes place in two stages. In the first stage, the multilayer
tube assembly is cooled in a water bath at a water temperature of
30° C. to 50° C., and in the second stage in a water bath
at a water temperature of 8° C. to 10° C.

[0063]After this controlled gradual cooling for the immediate hardening of
the outer polymeric layer 4, the multilayer tube assembly is conveyed to
a coiling system for the flexible tubes, or is cut and stocked in bundles
of straight lengths for the hard tubes. The finished multilayer tube
assembly may be tested electronically for possible defects (eddy
currents).

Production of the Multilayer Tube Assembly Using a Seamless Copper Tube 1
Having an Inner Diameter of 26 mm to 97.1 mm and a Wall Thickness of 0.50
mm to 1.50 mm

[0064]A seamless copper tube 1 (dimensions are given in Table 3) is
cleaned with solvents in order to remove any traces of lubricants, and is
afterwards conveyed to an induction type heater and heated inside the
induction type heater in atmospheric air to a temperature of 150°
C. to 250° C. Additionally, the seamless copper tube 1 passes
through a flame station comprising multiple flame nozzles around the
perimeter of the tube in order to oxidise the external surface. The
thickness of the oxide layer 2 is from 0.1 μm to 1.0 μm.

[0065]At this step, also the hardness of the seamless copper tube 1 is
reduced.

[0066]Subsequently the annealed seamless copper 1 tube having an oxide
layer 2 on its external surface is sufficiently cooled in ambient
atmosphere.

[0067]The seamless copper tube 1 is then passed through a first die, where
an adhesive component is extruded at an extrusion temperature of
200° C. to 230° C. through a primary extruder onto the
oxide layer on the external surface of The seamless copper tube 1, in
order to form an intermediate adhesive layer 3 having a thickness of 0.05
mm to 0.15 mm.

[0068]No forced cooling takes place after the extrusion of the
intermediate adhesive layer 3.

[0069]The seamless copper tube 1 directly proceeds to the second die,
where a polymeric component is extruded at an extrusion temperature of
210° C. to 250° C. through a secondary extruder onto the
intermediate adhesive layer 3 formed in the above step, in order to form
an outer polymeric layer 4. The thickness of the outer polymeric layer 4
is given in Table 4.

[0070]The second die is also called the finishing extrusion die, since it
controls the final outer layer of multilayer tube assembly.

[0071]In a special embodiment, the adhesive component and the polymeric
component may be co-extruded in a single extruder die.

[0072]In another special embodiment, copper oxides may be added to the
outer polymeric layer 4 in order to augment its thermal conductivity up
to at least 90 W/mK. The copper oxides may be incorporated in a polymeric
carrier resin and may be added in the form of pellets to the polymeric
component.

[0073]In a further special embodiment, external corrugations may be formed
on the outer polymeric layer 4 of the multilayer tube assembly through a)
specially designed extrusion dies, or b) through the use of embossed
rolls after extrusion has taken place.

[0074]Subsequent to the final extrusion cooling of the multilayer tube
assembly takes place in two stages. In the first stage, the multilayer
tube assembly is cooled in a water bath or by water sprays at a water
temperature of 30° C. to 50° C., and in the second stage in
a water bath or by water sprays at a water temperature of 8° C. to
10° C.

[0075]After this controlled gradual cooling for the immediate hardening of
the outer polymeric layer 4, the multilayer tube assembly is cut and
stocked in bundles of straight lengths. The finished multilayer tube
assembly may be tested electronically for possible defects (eddy
currents).

[0076]The adhesive component is a mix of linear low density polyethylene
(LLDPE) and a metal deactivator additive at a concentration of 1% to 2%.
The metal deactivator additive is a component itself of low density
polyethylene (LDPE) and a phenolic antioxidant at a concentration of 10%
(see FIG. 2).

[0077]The adhesive component forming the intermediate adhesive layer 3 has
maleic anhydride functionality that imparts polar characteristics to the
non-polar PE base resin. Maleic anhydride bonds to metal substrates by
creating both covalent and hydrogen bonds. Metal substrates generate
oxides on the surface. These oxides are further hydrolysed with water to
form hydroxyl groups on the metal surface. Maleic anhydride creates an
ester linkage (covalent bonding) to the OH groups on the surface. When
maleic anhydride rings open, they generate carboxyl groups. These
carboxyl groups bond to the oxides and the hydroxides on the metal
surface with hydrogen bonds.

[0079]PE-RT is an ethylene-octene copolymer specially developed for
resistance to temperatures up to 95° C.

[0080]The concentration of the metal deactivator in the polymeric
component is 1% to 2%. The metal deactivator additive is the same as the
one used in the adhesive component described above.

[0081]The concentration of the flame retardant additive in the polymeric
component is 1% to 2%. The flame retardant additive is a composition of
linear low density polyethylene (LLDPE) and an organic halogen-free flame
retardant at a concentration of 20%.

Metal Deactivator

[0082]The trade name of the metal deactivator additive is KRITILEN AO12.
The metal deactivator composition is shown in FIG. 4.

[0083]The active ingredient is a phenolic antioxidant
3-(4-hydroxy-3,5-ditert-butyl-phenyl)-N'-[3-(4-hydroxy-3,5-ditert-butyl-p-
henyl)propanoyl]propanehydrazide (CAS Number 32687-78-8) having the
structural formula given below.

##STR00001##

[0084]Polymers that come into contact with metals having low oxidation
potentials, such as copper, are susceptible to oxidation from the metal
catalysed decomposition of hydroperoxides. This is because ions of copper
are very active catalysts for hydroperoxide decomposition. Kritelen A012
is a phenolic antioxidant that interrupts the oxidation process by
binding ions into stable complexes though the donation of reactive
hydrogen and deactivates them.

Flame Retardant

[0085]The trade name of the flame retardant additive is KRITILEN FR240.
The flame retardant additive is a composition of linear low density
polyethylene (LLDPE) and an organic halogen free flame retardant at a
concentration of 20% as shown in FIG. 5.

[0086]The active ingredient is a triazine derivative having the chemical
name according to CAS: 1,3-Propanediamine, N,N''-1,2-ethanediylbis-,
reaction products with cyclohexane and peroxidized
N-butyl-2,2,6,6-tetramethyl-4-piperidinamine-2,4,6-trichloro-1,3,5-triazi-
ne reaction products

ADVANTAGES AND EFFECTS OF THE INVENTION

[0087]By the multilayer tube assembly of the present invention the
advantages of copper, such as mechanical strength, endurance at high
temperatures, stability at high work pressures, long service life, and
the like, are combined with the beneficial properties of the polymeric
component such as durability against corrosive environment as well as
resistance to external mechanical damages.

[0088]The improvement of its properties is moreover achieved by the strong
bond of the polymeric component to the seamless copper tube by means of
the adhesive component used between them, thereby behaving like a single
body.

[0089]In such a way, the seamless copper tube 1 carrying most of the
important mechanical properties of the multilayer tube assembly can
provide the same with a "shape memory", this is, it can be easily formed
by bending and maintaining its shape without the application of
significant manual strength. Moreover, due to the polymeric component the
multilayer tube assembly attains additional strength against temperature
fluctuations as well as thermal shock when used, for instance, in heating
installations.

[0090]In addition to the advantageous features of the oxide layer 2, the
metal deactivator additive and the flame retardant additive, the quality
of the outer polymeric layer 4 exhibits a particular advantageous effect,
because the PE-RT compound is specially developed to resist service
temperatures up to 95° C. This makes the resulting multilayer tube
assembly best suited for long term use in heating systems.

[0091]The addition of copper oxides to the outer polymeric layer 4
augments its thermal conductivity up to 90 W/mK. Thereby, the efficiency
of under-floor heating systems is increased. Moreover, the provision of
external corrugations on the outer polymeric layer 4 of the multilayer
tube assembly increases the area though which heat transfer takes place,
enhancing therefore the efficiency of under-floor heating systems.

INDUSTRIAL APPLICABILITY

[0092]The multilayer tube assembly of the present invention is suitable
for sanitary and heating installations. In cooling applications
(conditioners) it avoids the risk of condensation on the cold metallic
surface of the multilayer tube assembly, is highly suitable for
under-floor heating, because of the use of the special polymeric
component on the external surface as well as of the special adhesive
component, heating of high energy efficiency is achieved. This multilayer
tube assembly is also suitable for gas installations (coolants, fuels and
natural gas).

[0093]The multilayer tube assembly of the present invention is also
designed in a way to favour heat exchange in under-floor heating systems.

[0094]This multilayer tube assembly can have a length ranging between 2 m
and 300 m, an outside diameter between 14 mm and 110 mm and a wall
thickness ranging between 2.00 mm and 6.45 mm

[0095]The multilayer tube assembly of the present invention meets the
requirements of the "NSF-standard 61", and is therefore suitable for use
in drinking water networks.